1. Field of the Invention
This invention relates to a substrate support structure for an ion implantation device for supporting a substrate to be implanted with ions. Such a substrate support structure is used, for example, for production of semiconductor devices.
2. Description of the Prior Art
FIGS. 9 and 10 are schematic views of an ion implantation device such as one shown in page 457, Chap. 5 of "Ion Beams: with Applications to Ion Implantation" by R. G. Wilson and G. R. Brewer, published by J. John Wiley & Sons (1973). Semiconductor substrates 3 of silicon or the like to be implanted with ions by ion beams 1 are placed on a rotary disk 2. As shown, these semiconductor substrates 3 are arranged on the same circumference with the center at the rotary axis 5 of the rotary disk 2. Further, as shown in FIG. 10, each semiconductor substrate 3 is formed with grooves on its main surface.
The holding of the semiconductor substrates 3 on the rotary disk 2 is effected by a mechanical hold means (not shown) or by centrifugal force produced during rotation of the rotary disk 2.
The semiconductor substrates 3 arranged in the manner described above are irradiated with ion beams 3 and thereby implanted with ions of an impurity by an amount needed for production of semiconductor devices. The ion beams 1 usually have an acceleration energy of several tens KeV and their current value is at least several milliamperes. Therefore, if ion beams are directed continuously to a particular substrate, the amount of heat generated in the substrate would be too large. For this reason, the rotary disk 2 is rotated at a constant angular velocity .omega. so that individual semiconductor substrates are intermittently irradiated with ion beams. Thereby, the semiconductor substrates 3 are protected from being overheated.
It has been common practice to arrange the incidence of ion beams 1 to the semiconductor substrates 3 so that the ion beams are not perpendicular to the substrates in order to avoid the ion channeling phenomenon; they are inclined by about 10.degree. with respect to an axis perpendicular to the main surface of the semiconductor substrate 3, as shown by .theta. in FIG. 9.
However, in the case of the construction of the semiconductor substrates 3 having grooves 4 as shown in FIG. 10, the following problem arises.
The ion beams 1 are radiated also into the grooves. However, in the case where each groove is a rectangular parallelepiped defined by four lateral walls, all the lateral walls are not uniformly implanted with ions. More particularly, as shown in FIG. 10, the lateral wall disposed on one side is implanted with ions but the other lateral walls, i.e., those which are shadowed by the opening in the groove 4, are not implanted with ions. In FIG. 10, the regions 6 which are shadowed by the openings in the grooves 4 are shaded.